Palladium-catalyzed aqueous hydrodehalogenation in column reactors: Modeling of deactivation kinetics with sulfide and comparison of regenerants

Palladium (Pd) based catalysts are increasingly important in environmental applications; however, sulfide, a known poison, has been identified as a potential issue in laboratory and field studies. This paper develops a quantitative model for deactivation kinetics with aqueous sulfide; investigates the effects of pH on a catalyzed dehalogenation reaction and sulfide deactivation; and characterizes regeneration with acids, bases, and oxidizing agents. Results obtained with trichloroethylene show no inherent catalyst deactivation in deionized water. Deactivation increased with sulfide concentration and exposure time. Deactivation was slowly reversible by flushing the catalyst with deionized water at pH 10.4. Treatment with 20 mM sodium hypochlorite quickly and completely regenerated the catalyst, and was significantly more effective than hydroxide, hydrochloric acid, hydrogen peroxide, and air-saturated water. The time required for regeneration increased with increasing sulfide concentrations and exposure times. These results have important implications for maintaining catalyst activity with Pd or bimetallic catalyst systems.